Did a low reciprocating mass build in 5.56 a while back and it shoots very soft. I think the key was balancing everything, adjustable gas block, low mass BCG, weaker spring, and no weight in the buffer. Stays nice and flat, even less recoil, and once I got a proper ejector in it reliable with no malfunctions in at least a 1,000 rounds. Catch is all the special parts mean a more expensive build.